1. Field of the Invention
The present invention relates to a printing apparatus, a printing system, and a printing method in which images are printed by driving a plurality of print elements in a print head in a time divisional manner.
2. Description of the Related Art
Printing apparatuses based on an ink jet scheme (ink jet printing apparatuses; ink jet printers) have been prevailing widely which print images on a print medium such as a sheet by ejecting ink droplets from a plurality of ink ejection ports in a print head to the print medium. Known method for ejecting ink droplet from the ink ejection port uses electrothermal converter (heater) or piezo element. The electrothermal converter supplies thermal energy corresponding to a driving pulse to ink in a nozzle to form a bubble in the ink so that the resulting bubbling energy can be utilized to eject an ink droplet from the nozzle. An image is printed on the print medium by ejecting ink droplets from a large number of nozzles in accordance with print data.
Such an ink jet printing apparatus can print a high quality image at a high speed. Further, with the ink jet printing apparatus, the print head does not contact the print medium during image printing, allowing a high quality image to be stably printed regardless of the surface condition of the print medium.
One type of ink jet printing apparatus is what is called a full line type printing apparatus (line printer). This type of printing apparatus prints an image while consecutively transferring a print medium, enabling an increase in the speed at which an image is printed (image formation speed). Japanese Patent Laid-Open No. 2005-238556 describes a full line type printing apparatus using a plurality of print heads each having a large number of nozzles integrally formed thereon and forming ink ejection ports (multi nozzle heads). The print heads are arranged in parallel in a direction crossing the direction in which the print medium is transported and cooperate in ejecting ink to print an image.
Further, Japanese Patent Laid-Open No. 2001-246738 describes a configuration in which a large number of nozzles in a print head are divided into a plurality of blocks that are driven on the basis of different driving signals. The driving signals have the same waveform, provide different nozzle driving timings, and are each selected for use for one of the blocks. This allows the nozzles in each block to be driven in a time divisional manner, reducing the number of nozzles simultaneously driven. This in turn prevents a variation in ink ejection property caused by a variation in the driving load on the print head. More specifically, when one raster of image along the direction in which the nozzles are arranged is printed, varying the nozzle driving timing among the blocks enables a reduction in the drop of the driving voltage for the print head.
For the full line type ink jet printing apparatus, to avoid the interference between nozzles located close to each other, the nozzles in each block are desirably driven in a time divisional manner so as to sequentially drive the nozzles in the blocks not located close to each other. The interference between the nozzles located close to each other may be the adverse effect of a variation in ink pressure resulting from driving of one nozzle, on the ink in the other nozzle. Avoidance of the interference between the nozzles located close to each other makes it possible to stably print a high quality image.
On the other hand, if the nozzles are driven in a time divisional manner so as to sequentially drive the nozzles in the blocks not located close to each other, then within a print time required for one raster of image, the driving time may vary relatively significantly between the nozzles in the blocks located close to each other. Thus, when an image including a bar code or a ruled line is printed using the nozzles in the blocks located close to each other, the linearity of the bar code or ruled line may be impaired.